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Author Topic: 16 Bit Printing  (Read 48035 times)

cybis

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Re: 16 Bit Printing
« Reply #100 on: May 05, 2014, 03:00:03 pm »

Simple matrix profiles of RGB working spaces when plotted 3 dimensionally illustrate that they reach their maximum saturation at high luminance levels. But the opposite is the case with print (output) color spaces. Printers produce color by adding ink or some kind of colorant while working space profiles are based on building more saturation by adding more light due to the differences in subtractive and additive color models. To counter this, you need a really big RGB working space like ProPhoto RGB.

This is why PrinterRGB is a bit of a misnomer as it clips some dark cyans that the printer is able to reproduce. It's a significant improvement over AdobeRGB though, and probably a very reasonable compromise if your workflow narrows to 8-bit prematurely.
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digitaldog

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Re: 16 Bit Printing
« Reply #101 on: May 05, 2014, 03:02:41 pm »

This is why PrinterRGB is a bit of a misnomer as it clips some dark cyans that the printer is able to reproduce.
I have no idea what PrinterRGB is, never heard of it. But it sounds like you're saying it's a working space based profile and it's gamut is bigger than Adobe RGB (1998).
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cybis

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Re: 16 Bit Printing
« Reply #102 on: May 05, 2014, 03:21:35 pm »

I have no idea what PrinterRGB is, never heard of it. But it sounds like you're saying it's a working space based profile and it's gamut is bigger than Adobe RGB (1998).

It's that pRGB or PrinterRGB that popped up earlier in this conversation. It seems to be a new comer. It's included in the latest versions of Qimage. Can't seem to find much info about it. It's bigger than Adobe, smaller than ProPhoto and therefore clips the printer gamut just a bit.
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Ernst Dinkla

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Re: 16 Bit Printing
« Reply #103 on: May 06, 2014, 09:26:43 am »

Mike added dithering as the default in the latest version of Qimage Ultimate.

Ernst, op de lei getypt.
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cybis

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Re: 16 Bit Printing
« Reply #104 on: May 09, 2014, 11:17:19 pm »

To recap, here is my understanding of how LR, PS, and QI process 16-bit images for printing to an 8-bit printer driver, with color management done in-app.

Lightroom print module:
1.   Pixel size resampling.
2.   Output Sharpening.
3.   Color Profile conversion rounded to 20-bit -> dithered to 8-bit (semi-random dithering) at output resolution.

Photoshop print module:
1.   Color Profile conversion rounded to 20-bit -> dithered to 8-bit (semi-random dithering).
2.   No sharpening or resampling.
3.   Printer driver performs pixel size resampling.

Qimage Ultimate as of v2014.219:
1.   16-bit -> rounded to 9-bit -> dithered to 8 bit with repeating checkerboard pattern (non-semi-random) dithering.
2.   Pixel size resampling  (choices of interpolation methods).
3.   Output Sharpening (halo free DFS).
4.   Color Profile conversion rounded to 9-bit -> dithered to 8 bit with repeating checkerboard pattern (non-semi-random) dithering at output resolution.




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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #105 on: May 10, 2014, 08:56:11 am »

To recap, here is my understanding of how LR, PS, and QI process 16-bit images for printing to an 8-bit printer driver, with color management done in-app.

[...]

Qimage Ultimate as of v2014.219:
1.   16-bit -> rounded to 9-bit -> dithered to 8 bit with repeating checkerboard pattern (non-semi-random) dithering.
2.   Pixel size resampling  (choices of interpolation methods).
3.   Output Sharpening (halo free DFS).
4.   Color Profile conversion rounded to 9-bit -> dithered to 8 bit with repeating checkerboard pattern (non-semi-random) dithering at output resolution.

Hi Luc,

As far as I can see, it's:

Qimage Ultimate as of v2014.217:
1.   16-bit -> rounded to 8-bit.
2.   Pixel size resampling  (choices of interpolation methods).
3.   Output Sharpening (halo free DFS).
4.   Color Profile conversion rounded to 9-bit -> dithered to 8 bit with repeating checkerboard pattern (non-semi-random) dithering at output resolution.

Re 1. I cannot see any dithering in the imported image, e.g. you ramp, not even with a radius 1 and 2000% DFS sharpening in the image editor. It just accentuates the 1-bit transitions between the gradient steps. It would also be a bad thing because it could be enlarged by resampling and become visible with sharpening. Dithering is now the last thing that's applied during/after final colorspace conversion.

Re 4. I'm not 100% sure about the 'conversion rounded to 9-bit -> dithered' part, it may also be an option within the LCMS engine (I have not yet found a description of the built-in dither option on the LCMS website). Mike's remarks on his Techcorner are not explicit enough about the exact implementation, but he suggests 8-bit dithered to '512 virtual levels'.

The checkerbord dithering pattern may not be a bad choice since it is applied at the native printer resolution (600/720 PPI), and it avoids accidental clumping together with the printer driver's dithering patterns which are assumed to look rather stochastic.

Cheers,
Bart
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cybis

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Re: 16 Bit Printing
« Reply #106 on: May 10, 2014, 09:56:22 am »

Hi Bart,
check qu v219. Things change quickly. Mike added dithering in step 1. Also 9-bit give 512 levels.
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #107 on: May 10, 2014, 11:30:44 am »

Hi Bart,
check qu v219. Things change quickly. Mike added dithering in step 1. Also 9-bit give 512 levels.

Hi Luc,

Yes I have that version. It's not exactly clear what those new options do, so I left a question about that on Mike's Techcorner. I was wondering, since I cannot see any dithering on the imported 8-b/ch image. Maybe I have to look deeper somehow.

Cheers,
Bart

P.S. I had a closer look, and indeed the input conversion from 16-b/ch to 8-b/ch can now optionally be dithered. It has the checkered pattern (becomes faintly visible with excessive sharpening). I'll wait for Mike's answers on his techtalk forum.
« Last Edit: May 10, 2014, 02:19:00 pm by BartvanderWolf »
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alain

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Re: 16 Bit Printing
« Reply #108 on: May 18, 2014, 06:41:09 pm »

Hi

Has anybody tried a conversion from 16-bit prophoto to 16-bit pRGB (with RC not perceptual) before sending to Qimage?

Or a more general question : Is somebody using pRGB 16-bit as workspace versus prophoto 16-bit?

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jrsforums

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Re: 16 Bit Printing
« Reply #109 on: May 18, 2014, 06:52:16 pm »

Hi

Has anybody tried a conversion from 16-bit prophoto to 16-bit pRGB (with RC not perceptual) before sending to Qimage?

Or a more general question : Is somebody using pRGB 16-bit as workspace versus prophoto 16-bit?



Color space to color space conversions are, currently, always relative no matter what the settings.

I stay in prophoto while in LR and PS, plus plugins.  Before going to Qimage, I convert (export), in LR, to printerRGB 8bit TIFF.  
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John

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Re: 16 Bit Printing
« Reply #110 on: May 18, 2014, 07:37:17 pm »

Hi

Has anybody tried a conversion from 16-bit prophoto to 16-bit pRGB (with RC not perceptual) before sending to Qimage?

Hi Alain,

A two step profile conversion towards a smaller gamut (and the actually required current output profiles are much smaller) will most likely invoke two rounds of quantizing to smaller integer encoded colorspaces (PPRGB->pRGB->media/display RGB). It's probably safer to just do a single conversion at the end of the process. Whether it makes a visible difference in practice, depends on the actual colors encoded in the image data (with an even smaller required gamut than the output gamut) and print method (e.g. C-print is different from inkjet).

Quote
Or a more general question : Is somebody using pRGB 16-bit as workspace versus prophoto 16-bit?

I have used the Beta RGB for critical images (which is pretty close to pRGB in gamut but mainly with a different gamma encoding), i.e. images with very smooth gradients such as noise reduced sky or smooth seamless backgrounds. But one has to use it as a working space for all color/brightness/etc. corrections in the image editor! For such critical images, which I need to outsource (e.g. because of size), I first check what the actually required gamut is. Depending on the outsourcing partner, I'm occasionally told that I'm the first to ask for their output profile ...  One can use different tools for such an output profile  check, amongst others the excellent free Argyll CMS tools (in particular iccgamut.exe, tiffgamut.exe, and viewgam.exe).

Cheers,
Bart
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #111 on: May 18, 2014, 07:47:54 pm »

Color space to color space conversions are, currently, always relative no matter what the settings.

I stay in prophoto while in LR and PS, plus plugins.  Before going to Qimage, I convert (export), in LR, to printerRGB 8bit TIFF.  

Hi John,

Indeed, given that one cannot really select the working space profile in LR (it's Melissa RGB, the linear gamut version of ProPhoto RGB), that's generally safer than a two-step quantization.

For Qimage, if you only use a single output medium, it's even preferable to directly convert from LR to that output profile. Otherwise, an intermediate conversion from LR's linear gamma Melissa space to a narrower color-space that still covers all possible output media, such as pRGB or Beta RGB, makes sense.

Cheers,
Bart
« Last Edit: May 18, 2014, 07:49:56 pm by BartvanderWolf »
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Schewe

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Re: 16 Bit Printing
« Reply #112 on: May 19, 2014, 01:44:00 am »

(it's Melissa RGB, the linear gamut version of ProPhoto RGB)

Just to be clear, the actual working space of Lightroom is NOT "Melissa RGB". The only place where LR uses is to calculate the histogram and color readouts in the Develop module. Melissa RGB has ProPhoto RGB colors but with an sRGB tone curve (altered from the normal 2.2 gamma).

That actual internal working space is PhotoPhoto RGB colors and a linear gamma. To the best of my knowledge, Thomas has never actually given that color space a name.

I was around and involved in the decision to alter the histogram and color readouts to use the modified sRGB color space for display purposes...and Melissa Gaul asked why there weren't any color spaces with woman's names...so, by consensus, the LR engineering team decided to call that special color space "Melissa RGB"...

Wich unfortunately leads to some miscommunication because people seem to glom onto the "Melissa RGB" and think that's the internal working space, but it's not. The difference is in the gamma of the color space.

BTW, Melissa loves the fact she got a color space named after her (she deserves it) even though she's no longer working on LR.
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #113 on: May 19, 2014, 03:04:10 am »

Just to be clear, the actual working space of Lightroom is NOT "Melissa RGB". The only place where LR uses is to calculate the histogram and color readouts in the Develop module. Melissa RGB has ProPhoto RGB colors but with an sRGB tone curve (altered from the normal 2.2 gamma).

That actual internal working space is PhotoPhoto RGB colors and a linear gamma. To the best of my knowledge, Thomas has never actually given that color space a name.

Hi Jeff,

Thanks for the explanation.

Cheers,
Bart
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Ernst Dinkla

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Re: 16 Bit Printing
« Reply #114 on: May 19, 2014, 06:59:28 am »



For Qimage, if you only use a single output medium, it's even preferable to directly convert from LR to that output profile. Otherwise, an intermediate conversion from LR's linear gamma Melissa space to a narrower color-space that still covers all possible output media, such as pRGB or Beta RGB, makes sense.

Cheers,
Bart

Hello Bart,

I would expect at least two papers in use, gloss and matte, even for amateurs. True with no other goal than printing this (Tiff) file through Qimage Ultimate and then abandon it, it is a solution. I did not trust QU with QTR custom B&W profiles and used this method. The Qimage Ultimate extrapolation, sharpening etc happens after profile conversion then, which is not ideal or the file found better algorithms to requested printer resolution in another application before the profile conversion. For people that use Qimage Ultimate for image editing, even for minor adjustments (not my taste in both cases) it is not recommended either.

The second method I like more. If at the end of the RAW development one could export a 16 bit Tiff in pRGB to Qimage Ultimate, little would be lost and the file can be kept there for different jobs. But I wonder whether that still is a good idea if one imports it in Photoshop for more image editing on the 16 bit Tiff.  Is that gamut not just covering the best printers' gamuts? The PS edits may have an influence on the boundaries of that gamut which might not cover the best output gamuts as nice anymore?  With extended RAW developers like RawTherapee the route to a Tiff image editor is less needed, a RawTherapee pRGB conversion in the Tiff export can be done at best conditions if I interpret its features correctly.

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jrsforums

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Re: 16 Bit Printing
« Reply #115 on: May 19, 2014, 08:12:25 am »

Hello Bart,

I would expect at least two papers in use, gloss and matte, even for amateurs. True with no other goal than printing this (Tiff) file through Qimage Ultimate and then abandon it, it is a solution. I did not trust QU with QTR custom B&W profiles and used this method. The Qimage Ultimate extrapolation, sharpening etc happens after profile conversion then, which is not ideal or the file found better algorithms to requested printer resolution in another application before the profile conversion. For people that use Qimage Ultimate for image editing, even for minor adjustments (not my taste in both cases) it is not recommended either.

The second method I like more. If at the end of the RAW development one could export a 16 bit Tiff in pRGB to Qimage Ultimate, little would be lost and the file can be kept there for different jobs. But I wonder whether that still is a good idea if one imports it in Photoshop for more image editing on the 16 bit Tiff.  Is that gamut not just covering the best printers' gamuts? The PS edits may have an influence on the boundaries of that gamut which might not cover the best output gamuts as nice anymore?  With extended RAW developers like RawTherapee the route to a Tiff image editor is less needed, a RawTherapee pRGB conversion in the Tiff export can be done at best conditions if I interpret its features correctly.

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Ernst....

If I need further processing...in LR, PS, other editor....I go back to the 16 bit, PrpPhoto TIFF, which is still in LR, do the processing on it, which will create a new tiff, then export that to 8bit pRGB TIFF.

JOHN
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #116 on: May 19, 2014, 09:39:02 am »

The second method I like more. If at the end of the RAW development one could export a 16 bit Tiff in pRGB to Qimage Ultimate, little would be lost and the file can be kept there for different jobs. But I wonder whether that still is a good idea if one imports it in Photoshop for more image editing on the 16 bit Tiff.  Is that gamut not just covering the best printers' gamuts?

Hoi Ernst,

Yes, it's supposed to cover all printer media gamuts, but it's not nearly as small as an Adobe RGB gamut, it is instead still reasonably big. When I plot Adobe RGB, pRGB, and ProPhotoRGB colorspaces, the Argyll CMS 'Viewgam.exe' reports a gamut of:
1209647.5 cubic units for AdobeRGB 1998 (100% inside the pRGB colorspace),
1779999.8 cubic units for pRGB (68% intersected by AdobeRGB, so 32% larger, and 100% inside the ProphotoRGB colorspace),
2893604.8 cubic units for ProPhotoRGB (61.6% intersected by pRGB, so another 38.4% larger but partly imaginary 'colors').

Quote
The PS edits may have an influence on the boundaries of that gamut which might not cover the best output gamuts as nice anymore?

Yes, in theory one could push colors outside the pRGB gamut by editing, but it would not make sense to do so, because the colors cannot be printed. With a bit of luck, a perceptual rendering intent will pull them back into gamut, but also alter many other colors.

Luckily, it is rarely an issue because actual image colors in a file usually only occupy a small percentage of the full gamut of pRGB. Only those colors exactly on the axes of the primaries of the colorspace run a risk of being edited into an OOG color, others will just map to previously unused coordinates with lots of room to spare. It is really an eye-opener to see how little colorspace an image occupies.

To view it from another angle, Luc's 'torture_test.tiff' image, in ProPhotoRGB and with pushed saturation, intersects for  92.19% with the pRGB colorspace. Only a few very dark blue colors risk being clipped to marginally brighter very dark blue colors. In comparison, that image intersects for 92.22% with the ProPhotoRGB colorspace, only 0.03% additional colors are encoded, the rest of the coordinate space is unused and reserved for imaginary 'colors' we can't even see, and certainly not print/display, and with much coarser quantization steps to cover the (98.3% for nonexisting image colors) distance. The image only occupies 2.76% of the pRGB gamut, and 1.7% of the ProPhoto RGB colorspace.

pRGB is plenty large enough, but not insanely so.

Quote
With extended RAW developers like RawTherapee the route to a Tiff image editor is less needed, a RawTherapee pRGB conversion in the Tiff export can be done at best conditions if I interpret its features correctly.

Correct, but the risk of overcooking the colors remains very small, even with an additional editor step. pRGB offers hardly any downsides (why create an unprintable color anyway), but many upsides (more accurate, denser quantization, less risk of posterization in an 8-bit pipeline). The added dithering in Qimage reduces the posterization risks even further.

Cheers,
Bart
« Last Edit: May 19, 2014, 09:41:34 am by BartvanderWolf »
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #117 on: May 19, 2014, 09:58:44 am »

Ernst....

If I need further processing...in LR, PS, other editor....I go back to the 16 bit, PrpPhoto TIFF, which is still in LR, do the processing on it, which will create a new tiff, then export that to 8bit pRGB TIFF.

Hi John,

Yes, you are using a correct print output workflow. By outputting an 8-b/ch file, Qimage then optionally only dithers at the very last colorspace conversion step after output sharpening, adding a virtual 9th bit to the pipeline. With a 16-b/ch input image it optionally dithers both at the 16 to 8-b/ch conversion and at the final colorspace conversion. Since Qimage usually prints at 600/720 PPI resolution, the final dither is beyond human visual acuity, it can only help.

Cheers,
Bart
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cybis

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Re: 16 Bit Printing
« Reply #118 on: May 19, 2014, 10:12:12 am »

Hi John,
Yes, you are using a correct print output workflow. By outputting an 8-b/ch file, Qimage then optionally only dithers at the very last colorspace conversion step after output sharpening, adding a virtual 9th bit to the pipeline. With a 16-b/ch input image it optionally dithers both at the 16 to 8-b/ch conversion and at the final colorspace conversion. Since Qimage usually prints at 600/720 PPI resolution, the final dither is beyond human visual acuity, it can only help.

To be clear, note that doing the 16-bit>8-bit conversion in LR also introduces dithering which will be enlarged and sharpened in QU (although the dithering algorithm QU and LR are very different.)
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Bart_van_der_Wolf

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Re: 16 Bit Printing
« Reply #119 on: May 19, 2014, 10:40:30 am »

Hi folks,

I'm not sure if the attached VRML file is allowed as file type, but for those who have a VRML viewer plugin (e.g. one from the Cortona3D viewer page) installed in their browser one can display, zoom, and rotate the colorspace hulls in 3D (solid for the smaller gamut and wireframe for the larger gamut colorspace).

It shows that the pRGB colorspace adds a more saturated gamut and specifically darker colors to AdobeRGB, yet covers a reasonably large part of the excessively-large ProPhoto RGB.

Cheers,
Bart
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